I've been riding this CBR250R 88 model for 4 months now with little trouble, until now. It all didn't start on a cold Friday when I wanted to go for a ride, the day before, the bike started in the same conditions without effort.

Tried a rolling start, jumper starter, electronics seemed to be ok. After a few tries at this all that happened was backfiring. The next day, I proceeded to strip down the bike, checking connections and stuff. All sparkplugs seemed to be sparking, so i pulled apart the carby for clean, which went well. Through it all back together to no result expect it doesn't backfire.

Any help, ideas or information would be greatly appreciated.

ADD: the starter motor kicks the engine over but not much more then that.

 

My guess would be a new set of plugs. In cold conditions, plugs foul really easy. Even if you have spark, once they foul, they won't spark in the combustion chamber under compression. the ignition system on motorcycles is very weak and a weak plug won't fire correctly. And, once these little plugs foul, they are pretty much junk, drying them out does very little for them. about your only course of action is a new set of plugs. Also, when you get the bike running again, give the bike extra time to warm up before hopping on and going. They need a lot of time to fully warm up.

 

just changed the plugs, no result

 

usually, sparkplugs will backfire the bike when they are fouled. Since you pulled apart the carbs and cleaned them, then the backfiring stopped, makes me think your not getting gas now since the cleaning.

I don't know your ability, so its hard to suggest if the cleaning was done properly. One mistake quite a few people make when cleaning the carb is they do not reset the air/fuel screw properly. They usually just screw it all the way in, which is not correct. it should be anywhere from one and a half to two turns out from bottom. If it is fully seated, there won't be any fuel entering the port.

I would first see if your getting fuel to your carb, as in there is fuel in the float bowl. If there is, check your adjustments.

A quick way to see if your getting fuel or not is to buy a can of starting fluid, spray a few squirts into the end of the carb with the throttle open, then shut the throttle and crank it over. If it fires, you have a fuel starvation issue.